1. Field of the Invention
The present invention relates to a sensor control apparatus, a sensor control system, and a sensor control method.
2. Description of the Related Art
For internal combustion engines such as a diesel engine and a gasoline engine, it is common to control a mixture ratio (i.e., a ratio of gas to fuel which is supplied to each combustion chamber) in order to reduce fuel consumption and purify exhaust gas. In order to control the mixture ratio, a gas sensor is used to measure the proportion of a specific gas component (e.g., oxygen) contained in intake gas or the proportion of a specific gas component contained in exhaust gas.
The gas sensor includes a sensor element disposed in a gas which is a target for measurement (hereinafter referred to as an object gas). The sensor element outputs a value representing the concentration of a specific gas component (e.g., oxygen concentration), which is the proportion of the specific gas component. However, the value output from the sensor element is known to be affected not only by the concentration of the specific gas component of the object gas but also by the pressure of the object gas.
In recent years, since the degree of fineness of control of an internal combustion engine has increased, there is an increasing need for measuring the concentration of a specific gas component more accurately. In order to measure the concentration of a specific gas component of an object gas more accurately, various methods have been proposed for eliminating the influence of the gas pressure on the value output from the gas sensor (see, for example, Patent Documents 1 and 2).
Patent Documents 1 and 2 disclose a configuration including a sensor element which measures the concentration of a specific gas component of an object gas and a pressure sensor which measures the pressure of the object gas. In addition, Patent Documents 1 and 2 have proposed a method (correction method) for eliminating the influence of the gas pressure on the value which is output from the gas sensor and which represents the concentration of the specific gas component. In this method, the value output from the gas sensor is multiplied by a coefficient based on the pressure measured by the pressure sensor, whereby the influence of the gas pressure on the output value is eliminated.
[Patent Document 1] Japanese Patent Application Laid-Open (kokai) No. H6-273381
[Patent Document 2] Japanese Patent Application Laid-Open (kokai) No. 2005-061420